I put 4 Home Depot N:vision spirals in a Spiderlite softbox. The results look good so far with the 5500k bulbs. The spiderlite holds five bulbs so the center bulb is squeezed by the four adjacent bulbs, in fact there's glass to glass contact. So I'm thinking I should put the other, loop styled CFL in the center socket. I don't think Nvision makes the other loop style, so a different brand, provided the temp in within 100k should blend in with the four N:visions?

Normally that should be the case as long as the CRI of all of them are relatively high. The CRI of the N:Visions is about 80 which is tolerable and as long as whatever else you put in there is also about 80 and about the same color temperature within 200 to 400, it should be fine. Color temperature differences in the daylight range are not as noticeable as in the 2900K to 3200K range.